This invention is directed to a buzzer assembly for use in a personal communications device which changes geometry in order to emit sounds at a variety of frequencies at an approximately constant volume, such as for playing melodic alerts.
Personal communications devices, such as cellular phones or pagers, typically have a number of components which help to alert the user to various conditions. For instance, an alert may be generated in response to an incoming call or page. The most common alert generating components are vibrators and buzzers, of which buzzers are of interest for the present invention.
Typically, buzzers resonate at a ring frequency around three kilohertz, producing a simple monotone alert sound or a dual tone of closely spaced frequencies. Problems arise when, instead of a simple monotone, users desire alert sounds to be other than monotone or tightly spaced dual tone, such as a melody that varies frequency over the range from about 1 kHz to about 4 kHz. Typically, buzzers are configured for optimum audio output at a particular frequency (the "ring frequency"). When such a buzzer is used at other frequencies, the buzzer output volume drops off significantly, even at frequencies as close as 200 Hz away from the ring frequency. This results in an unrecognizable melody with significant disparities in volume while the "melody" is played. This variability in loudness reduces the perceived quality, can be annoying to the user, and may result in missed calls.
The immediately apparent solution of using a larger buzzer capable of generating sufficient volume at different frequencies is not practical due to the extreme space constraint pressures present in today's world of ever shrinking personal communications devices.
It is known in the art to combine a vibrator, speaker and buzzer into one unit, called a multi-mode actuator. While such multi-mode actuators can be used to play melodies, they suffer from a serious drawback. The output from the multi-mode actuator in speaker mode should be directed into the user's ear for optimum performance. However, because the audio volume in call alert mode is much higher than in speaker mode, the output of the multi-mode actuator should not be directed into the user's ear. Thus, the optimum output routing configuration for the multi-mode actuator is different for its different functions, thereby defeating its combinational advantage. As such, it is common to use a separate buzzer whose output is typically vented perpendicular to the plane of the speaker that is used to output audio signals from the personal communications device. In this manner, the output from the buzzer is not directed into the user's ear in the event a user places the device against their ear immediately prior to an alert. However, due to existing buzzers' inherent output audio volume variation over frequency, as mentioned above, existing buzzers perform poorly when asked to play melodies, rather than a monotone, for alert signals.
As such, there remains a need for an improved buzzer assembly for use with portable communications devices that produces an acceptable level of audio volume across a broader frequency range, so as to be able to play melodies and the like for alert signals.